<template>
  <div class="scrollText" ref="outer">
    <div class="st-inner" :class="{'st-scrolling': needToScroll}">
      <!-- 加两条是为了滚动的时候实现无缝衔接 -->
      <span class="st-section" ref="inner" v-html="content"/>
      <span class="st-section" v-if="needToScroll" v-html="content"/>
    </div>
  </div>
</template>
<script>
export default {
  name: 'ScrollX',
  data() {
    return {
      needToScroll: false,
      text: ''
    }
  },
  props: {
    content: {
      default: "",
    },
    pageDuration: {
      default: 8,
    },
  },
  mounted() {
    this.startCheck()
  },
  beforeDestroy() {
    this.stopCheck()
  },
  methods: {
    // 检查当前元素是否需要滚动
    check() {
      this.setText()
      this.$nextTick(() => {
        this.needToScroll = this.isOverflow()
      })
    },

    // 判断子元素宽度是否大于父元素宽度，超出则需要滚动，否则不滚动
    isOverflow() {
      let outer = this.$refs.outer;
      let inner = this.$refs.inner;
      let outerWidth = null
      let innerWidth = null
      if(!!outer&&!!inner){
        outerWidth = this.getWidth(outer)
        innerWidth = this.getWidth(inner)
      }
      return innerWidth > outerWidth
    },

    // 获取元素宽度
    getWidth(el) {
      let {width} = el.getBoundingClientRect()
      return width
    },

    // 获取到父组件传过来的内容复传给this.text
    setText() {
      this.text = (this.$slots.default && this.$slots.default.reduce((res, it) => res + it.text, '')) || ''
    },

    // 增加定时器，隔一秒check一次
    startCheck() {
      this._checkTimer = setInterval(this.check, 1000)
      this.check()
    },

    // 关闭定时器
    stopCheck() {
      clearInterval(this._checkTimer)
    }
  }
}
</script>
<style lang="scss">

.scrollText {
  overflow: hidden;
  white-space: nowrap;
}

.st-inner {
  display: inline-block;
}

.st-scrolling .st-section {
  padding: 0 5px;
}

// 向左匀速滚动动画
.st-scrolling {
  animation: scroll 10s linear infinite;
}

@keyframes scroll {
  0% {
    transform: translate3d(0%, 0, 0);
  }
  100% {
    transform: translate3d(-50%, 0, 0);
  }
}
</style>